Stents are essentially metal armatures which are inserted without surgery into arteries as bypasses against the development of intimal hyperplasia, angiopathy occlusions and other disorders affecting arterial ducts. These armatures may be lattice elements in a metal alloy with a thermal memory, ie. in shape, and are flexible, strong, biocompatible, self-expanding, radio-opaque, and able to regain their shape even when overextended.
To be used, a stent with shape memory is first tightened and closed, at a low temperature, in a sheath with such dimensions as to be able to pass into an arterial duct. Then, once introduced into the artery, it is released and, with the body temperature, it regains its original shape,
Mechanical-expansion metal armatures are likewise known foe implantation in arterial ducts.
Such armatures, once taken in their contracted form into the desired section of an artery, are expanded, for example, by means of an inflatable ball inserted into the duct along with the armature.
However, though the above mentioned type of stent is available, a reliable technique for inserting it into the arterial duct has not yet been established. At present, to insert a stent into an arterial duct, catheters of a conventional type for arterial treatment and exploration are used. The stent is placed and tightened in a sheath, arranged inside the insertion catheter, carried with this to the area of implantation in an artery and mechanically released by pushing it out of the sheath with a thread extending into the catheter. This technique has however problems of insertion, due to the necessary force which is difficult to transmit over a distance with a flexible hose.